With the recent progress of photographic technology, silver halide light-sensitive materials have attained remarkable improvement in both sensitivity and image quality. On the other hand, consumers' needs for a light-sensitive material have been more diversified than ever. Under such circumstance, a silver halide emulsion with improved gradation controllability has been acquiring importance. At the same time, there has been an increasing demand for a silver halide emulsion capable of providing excellent photographic properties irrespective of the variation of processing conditions such as developer temperature and development time.
As a method for obtaining a silver halide photographic light-sensitive material with improved sensitivity and image quality, Japanese Patent Publication Open to Public Inspection (hereinafter referred to as Japanese Patent O.P.I. Publication) No. 113934/1983 discloses the use of an emulsion comprising tabular silver halide grains having a grain diameter/grain thickness ratio of not less than 8, and Japanese Patent O.P.I. publication No. 143331/1985 disclosed the use of an emulsion comprising core/shell type silver halide grains each having a silver iodide-rich portion in the inside thereof.
These emulsions are defective in processability. In the case of the former emulsion, due to its tabular shape, the grain has an excessively high development activity in spite of its average silver iodide content, which makes it difficult to obtain a prescribed gradation. This emulsion is also poor in graininess.
Though improved in graininess, the latter emulsion cannot have such "a high development activity" as described in the specification as the effect of the invention. Contrary to the description in the specification, the grain contained in this emulsion has a poor development activity due to its high silver iodide content, which makes the emulsion have a poor gradation controllability. Efforts to enhance development activity by decreasing the average silver iodide content of a grain result in a lowered sensitivity.
By the preceding conventional techniques, it is impossible to obtain a silver halide emulsion having an appropriate development activity which permits easier gradation control for a prescribed development time, while maintaining sensitivity and graininess at higher levels.